Known techniques for controlling molten metal flow from ladles, crucibles, and like vessels generally rely on the use of stoppers mechanically positionable in the discharge nozzle. Typical is the device disclosed in U.S. Pat. No. 3,200,457 to Wagstaff. Also, in U.S. Pat. No. 3,253,307 to Griffiths et al, there is disclosed a plug at the end of a shiftable stopper for seating in the discharge nozzle of the vessel.
Disclosure in U.S. Pat. No. 4,199,087 to Golas et al relates to a further exemplary stopper in the form of a sliding gate valve. A cut-off gate slides across the passage through which molten metal is otherwise dischargeable from the vessel.
Also included in the disclosure of the foregoing patents is the concept of use of pressurized gas to regulate the discharge of the molten metal through the nozzle. Griffiths et al is of particular interest in its disclosure of gas injected into the nozzle orifice uniformly around the periphery of the orifice. This action confines and reduces the diameter of the stream, and thus reduces the rate of metal discharge. Nonetheless, the Griffiths et al application of the gas to the casting nozzle is not intended to control the full on and off flow of the molten metal. To the contrary, Griffiths et al specify that the gas injection rate remains below that at which irregularity or breakup of the streamline flow of molten metal through the nozzle occurs.
The prior art thus fails to provide a gas pressure on-off control of molten metal flow. Utilization of gas pressure in the known prior art of molten metal feed is clearly directed only to regulating a sustained flow with reliance on mechanically operated devices to cut off such flow.